The present invention relates generally to the art of pyrolytic deposition of metal-containing films, and more particularly to the pyrolytic deposition of metal oxide films from aqueous compositions of coating reactants.
The pyrolytic deposition of metal oxide films onto a glass surface is described in U.S. Pat. No. 3,660,061 to Donley et al. Organometallic salts, preferably acetylacetonates, are dissolved in an organic vehicle such as methylene chloride. Other suitable solvents include aliphatic and olefinic halocarbons, halogenated hydrocarbons, alcohols, and nonpolar aromatic compounds such as benzene and toluene. The organic solution is sprayed onto a hot glass surface where it thermally decomposes to form a metal oxide film which alters the reflectance and transmittance of solar energy by the glass.
Current interest in eliminating the health and environmental hazards of using large volumes of organic solvents has encouraged the development of aqueous coating compositions. It is known from U.S. Pat. No. 2,688,565 to Raymond that light reflecting coatings of cobalt oxide may be deposited by contacting a hot glass surface with an aqueous solution of cobalt acetate. However, such films have a grainy, irregular texture and are highly porous, resulting in poor acid resistance evidenced by debonding of the film.
U.S. Pat. No. 4,308,319 to Michelotti et al discloses the pyrolytic deposition of a durable, uniform, solar energy reflecting spinel-type film from an aqueous solution of a water soluble cobalt salt and a water soluble tin compound. In a development related to the present invention, U.S. patent application Ser. No. 463,194 filed on even date herewith by C. B. Greenberg discloses a method for depositing metal-containing films from aqueous compositions wherein ultrafine powder coating reactants are chemically suspended in an aqueous medium comprising a chemical wetting agent to form an aqueous chemical suspension which does not require constant vigorous agitation.